Method and apparatus for grinding solid particles



E. R. HALLER Sept. 7, 1965 METHOD AND APPARATUS FOR GRINDING SOLID PARTICLES 3 Sheets-Sheet 1 Filed Feb. 28, 1963 fem-s7 Kama-fir 641: 1 5? E. R. HALLER.

Sept. 7, 1965 3 Sheets-Sheet 2 Filed Feb. 28, 1963 Sept. 7, 1965 E.-R. HALLER 3,204,880

METHOD AND APPARATUS FOR GRINDING SOLID PARTICLES Filed Feb. 28, 1965 S Sheets-Sheet 3 [P/var Keefer #411 5A r 3,204,83fi Ice Patented Sept. 7, 1965 3,204,880 METHOD AND APPARATUS FOR GRINDING SOLID PARTICLES Ernest R. Heller, Geneva, Switzerland, assignor to Stecco, Socit Anonyrne de Technique Chimique, Geneva, Switzerland, a corporation of Switzerland Filed Feb. 28, 1963, Ser. No. 261,649 (Claims priority, application Switzerland, Mar. 5, 1962, 2,691/62 4 Claims. (Cl. 241-29) The present invention relates to the grinding of solid particles in order to bring them to a predetermined fineness which is as uniform as possible. It is more particularly applied to pigments employed in the manufacture of colouring materials, but it may also be utilized for other products for various purposes.

It is known that in order to obtain by grinding solid particles of pre-determined size, irrespective of the type of grinding machine used, a single pass through the grinder is insufiicient. This single pass gives a mixture of particles of different sizes, of which some may comply with the fineness required, while the others are too large.

In order to overcome this disadvantage, it is the usual practice to employ a number of successive passes through the grinder. In general, in order to carry out these successive passes in a convenient and continuous manner, a re-cycling procedure is adopted, that is to say the Whole mass is carried through in one cycle of multiple passes into the grinder, while extracting a portion in a continuous manner, this extraction being compensated by a further introduction of the product to be ground.

Following this process, there is obtained in the extraction from the re-cycled mass, after a certain number of cycles, a granular size the average value of which can be considered as complying with the required degree of fineness. However, this method of operation has the disadvantage of introducing relatively large particles into the continuous cycle, a portion of these large particles roe-appearing in the final product without having been subjected to a sufiicient number of passes. In other words, if the mean value of the particles obtained complies with the desired fineness, this is at the cost of a sometimes excessive spread-over of the granular sizes, the product including elements which are insufiiciently ground.

The remedy for this diificulty is known; it consists of abandoning both the re-cycling and the continuity of the process, and subjecting the whole of the treated material to successive passes thorugh the grinder without introduc tion of raw material, and without intermediate extraction. This discontinuous method of operation ensures a more reliable result in respect of the fineness and the granulometric uniformity of the final product, but it results in complication of the operations, in more careful supervison, and necessitates substantially more personnel.

The present invention has for its object, in a method of grinding utilizing a number of discontinuous passes, to limit the above drawbacks and to provide the advantages of operation with continuous re-cycling, with a more uniform granular size.

The invention ischaracterized in that, in the grinding machine in continuous operation, distinct successive passes of the whole of the material to be ground are carried out, these passes being initiated automatically, following a pre-determined programme.

According to this method, a fresh pass into the grinding machine can only be started after the whole of the "material ground during the preceding pass has passed passes producing its appropriate degree of fineness. It is therefore by a sequence of discontinuous operations that complete grinding is obtained. These operations are however carried out automatically without any manual action, so that there is obtained in this way an automatic cycling by discontinuous passes.

The automatic operation of the successive passes in accordance with the pre-established programme is effected by a set of valves operated by relays actuated according to the indications of level-indicators in the tanks which receive the material under treatment.

This material, normally in the form of a dispersion in an appropriateliquid, is handled by pumps, and the set of valves according to the programme provides the suit able successive circuits which bring the dispersion to the grinding machine.

At every stage of the operation and at every pass, a check of the graular size obtained can be carried out and the size and particularly the uniformity of sizes of the particles can be verified.

The method of carrying the invention into effect will be more fully described with reference to the accompanying drawings. In these drawings:

FIG. 1 is a general view in perspective of the grinding installation.

FIG. 2 is a View in cross-section of a tank of FIG. 1.

FIG. 3 is a diagram explaining the manner in which the successive passes are carried out.

FIG. 4 shows the arrangement of the electrical equipment which controls the circulation channels.

In order to carry out the method of grinding by successive passes, there is employed an installation such as that shown by way of example in FIG. 1. This installation is essentially composed of a grinding machine 1 and three tanks 2, 3 and 4.

The grinder 1 can be of any conventional type with balls, discs, cylinder, sand, etc. In the arrangement shown, this grinder is of the vertical-shaft type mounted on a support 5 and driven by a motor 6 which is mounted on the frame 7.

The tank 2, which will subsequently be known as the pre-mixing tank, is provided with a two-speed agitator 8, driven by a reduction gear 9. The tank 3, which will subsequently be known as the re-cycling tank, is provided with an agitator 10 having a single speed, driven by the motor-reduction gear 11. The third tank 4, known as the finishing tank, is also provided with an agitator 12 driven by the motor-reduction gear 13.

Each of the tanks is equipped substantially as shown in FIG. 2. The latter shows a cross-section of the premixing tank 2. With the tank proper is associated a casing 14 providing for a circulation of cooling water; 15 is the water inlet and 16 is its outlet.

In the vicinity of the domed bottom 17 are arranged on the one hand the evacuation pipe 18 to which is connected the piping from the circulation pump, and on the other hand the pipe 19 of the rinsing valve. The filling pipe has its outlet at 20.

An intermediate tank 21 (FIGS. 1 and 3) is associated with the grinding machine 1. This tank, intended to receive the product passing out of the grinder through the overflow outlet 22, comprises at 23 a filter intended to retain the balls or the grinding sand which may be carried away with the ground material.

The circulation of the material to be ground is effected by two pumps 24 and 25, driven by a motor group 26. On the drive of the pump 25 is provided an electro-magnetic clutch 56.

The suction of the pump 24 is coupled through a piping 27, on the one hand at 28 to the tank 2 and on the other hand at 29 to the tank 3. Valves 30 and 31 are respectively arranged on the pipes 28 and 29. The

pump 24 delivers into the grinder 1 through the pipe 32.

This pipe 32 is provided with a stop-valve 33.

The pump 25 is under the head due to the intermediate tank 21 through the pipe 34. This pump 25 delivers into the piping 35, which is provided at 36 with a threeway device which directs the'circulating material into one of the pipes 37, 38 or 39; 37 to the tank 2, 38 to the tank 3 and 39 to the tank 4.

The device 36 may be arranged so as to ensure the orientation of the circulation. This orientation can however also be obtained by means of valves 40, '41 and 42, provided on the piping systems 37, 38 and 39.

The control of the various valves is effected automatically by a series of electric contacts. These valves are preferably of the diaphragm type actuated by compressed air and controlled by electric relays. The whole of the control of the valves is effected by a programming device. The initiation and control of the operations are effected from a control desk 43 (FIG. '1).

The cycle of the operations and the control of the circulation are operated by electric probes mounted in the tanks 2, 3 and 21. The tank 2 is provided with two probes 44 and 45; the probe 44 in the vicinity of the bot tom of the tank (FIGS. 2 and 3), the probe 45 below the level of the agitator 8. The tank 3 is provided with a probe 46 close to the bottom. The tank 21 has two probes 47 and 48, one close to the bottom and the other at the upper portion.

Through an appropriate electrical arrangement, the probes 44 and 46 control the starting of a motor 49 (FIG. 4), the shaft of which is provided with a succession of earns 50, 51, 52 and 53. The probe 45 stops the motor of the agitator 8 when the level falls below that of the agitator. The probes 47 and 48 control the electro-magnetic clutch 56 of the .pump 25. Each of the cams is in contact with the push-rod 54 of a contact 55, as shown by the broken away portion of the contact of the cam 50. These contacts operate the relays which control the actuation of the valves.

In order to carry out the grinding of a suspension of solid materials, for example pigments, the tank 2 is filled with this suspension. The suspension is first deflocculated by putting the agitator 8 into action at high speed.

After a pre-determined time, an automatic time-switch changes the agitator to low speed and then stops it until the froth which may have formed has subsided.

When the de-flocculation is completed, the pump 24 is started-up and the valve 30 is automatically opened. The pump sucks-in the suspension and delivers it into the grinding machine 1.

The tank 2 thus empties gradually. When its level has reached the probe 45, the latter operates the stopping of the agitator 8. When the level falls to that of the probe 44, the programming device comes into action and reverses the circuit.

After the passage of the material pumped into the grinding machine 1, it passes into the intermediate tank from which it is drawn in by the pump 25 so as to be delivered into the tank 3 through 35 and 38, the valve 41 being open.

When the probe 44 has given the appropriate signal, the set of valves is reversed. The valves 30 and 41 are closed, the valves 31 and 40 are opened. This opening is effected by rotation through half a revolution of the cams 50 to 53 which actuate the contacts 55.

There then begins the second passage from the tank 3 to the tank 2 through the grinder 1. The contents of the tank 3, sucked in by the pump 24 through 29-27, is delivered into the grinder 1 and the ground material which reaches the intermediate tank 21 is drawn-in by the pump 25 and delivered through 35 and 37 to the tank 2. When the level in the tank 3 has fallen to that .of the probe 46 the latter effects the initiation of the reversal of the circuits, following a process similar to that previously described for the earns 50 to 53.

The tank 2 is again filled and the tank 3 is empty. A fresh cycle begins and so on. In this way, an appropriate number of successive passes from 2 towards 3 and from 3 towards 4 is obtained, with intermediate grinding at 1. When the number of passes is sufficient to give the desired fineness, the valve 42 is opened and the valves 40 and 41 are closed. The treated material is then directed at 39 into the finishing tank 40, from which it is collected.

The opening of the valve 40 is initiated by a predetermining counter which counts the successive cycles.

The probes 47 and 48 of the tank 21 have the object of maintaining permanently a certain quantity of product in the said tank, in order to prevent the pump 25 from drawing air into the circuits. The stopping of the pump 25 takes place if the level in 21 falls below the probe 47, in order to prevent the pump 25 from working when empty. The probe 48 starts up the pump 25 again when the level in 21 rises to that of probe 48. The stopping is effected by the release of the electro-magnetic clutch 56 of the pump 25.

Safety devices are provided in addition, in order to stop the whole installation in the event of an untoward incident of any kind.

EXAMPLES Example 1 20 kgs. dry weight of a pulp obtained from a filter press of a pigment resulting from the copulation of diazotized meta-nitro-para-toluidine, and copulated on acetyl-aceto-anilide, and complying with the following formula:

is put in dispersion with kgs. of water and the necessary dispersing agent in the apparatus described above, and about 20 passes through the machine are carried out until a granulation is obtained between 0.5 m and 1 micron and verifiable by a microscope with respect to a previously-made tube which gives the size of particle which is acceptable for the coloration of viscose (cellulose xanthate). The product thus obtained is put into dispersion in viscose by two methods:

(a) In the mixer at the moment of the formation of the cellulose alkali;

'(b) By blowing into the viscose before its extrusion through the dies.

There is then obtained a viscose which is coloured all through the mass, the strength of which is excellent and permits of its use in the manufacture of textiles for various applications.

Example 2 NO OQHN are put in reaction in the apparatus with kgs. of 1.4 dioxane and a small proportion of hydrogenated colophony as the dispersing agent.

Example 3 50 kgs. of phthalo-cyanine blue of the alpha form, ob-

tained in accordance with the following composition: 336 kgs. of trichloro-benzene serving as a solvent for the following products:

84 kgs. of phthalic anhydride; 135 kgs. of urea;

15.7 kgs. of cuprous chloride; 2.2 kgs. of amonium molybdate;

after treatment in a reactor at the appropriate temperature, a solution in sulphuric acid and re-precipitation with water are dispersed in the apparatus above-described with 25 kgs. of water and the necessary quantity of dispersing agent.

The dispersion is then subjected to the method of discontinuous cycling for 3 cycles, the covering power being verified according to the usual standards, in order to bring the blue to a uniform state of granulation permitting the best covering power to be obtained.

This dispersion is then added to an emulsion of vinyl acetate containing the chemical products necessary for the manufacture of a paint. There is thus obtained a paint of indoor or outdoor quality having a very strong resistance to light, a maximum covering power and an excellent colour efiiciency.

Example 4 There is put into the apparatus 30 kgs. of sulphur in dispersion in 150 litres of water and there are then carried out discontinuous cyclings following the process indicated above, with the desired dispersing agent.

The emulsion thus obtained is poured into a Werner- Pfeiderer apparatus under vacuum or alternatively the emulsion is atomized in an atomization chamber until a powder is obtained which, When diluted in water, can serve as a highly-active pepticide product.

Example 5 32 kgs. of acetyl salicylic acid are put into dispersion with 68 kgs. of water in the apparatus which has been described above. This dispersion is treated in the apparatus described until a molecular division of about 0.5 mg is obtained.

1 kg. of an active cation dispersing agent is put into reaction in the aqueous solution containing the acetyl salicylic acid, so as to prevent the molecular reagglomeration of the dispersion obtained. The latter is dried in an apparatus under vacuum or by an atomizer. There is obtained a substance which can be utilized from the physiological point of view without giving rise to the difliculties due to the contact of too-large granulations of this product on the mucous membranes.

What I claim is:

1. A method of grinding solid particles in a plurality of repeating cycles, comprising placing the material to be ground in suspension in a liquid in a first receptacle, passing the material from the first receptacle into a grinder until the 'first receptacle is substantially empty, collecting the material from the grinder in a second receptacle, passing the material from the second receptacle back into the grinder until the second receptacle is substantially empty, and passing the material from the grinder back into the first receptacle.

2. Grinding apparatus comprising a grinder, two receptacles for receiving the material to be ground, conduit means connecting the grinder with each of the two receptacles, valve means for directing the material alternately through the conduit means from the first receptacle through the grinder to the second receptacle and from the second receptacle through the grinder to the first receptacle, and means responsive to the level of the material in the first and second receptacles to actuate the valve means alternately to fill and empty the first and second receptacles.

3. Apparatus as claimed in claim 2, the last named means comprising detector means in the first and second receptacles for detecting the level of material therein.

4. Apparatus as claimed in claim 2, and counter means for counting the number of cycles, and means responsive to a predetermined setting of the counter means for discontinuing operation upon the completion of said predetermined number of cycles.

References Cited by the Examiner UNITED STATES PATENTS 1,265,809 5/18 Navarre 241-97 1,291,877 1/19 'Herrbold 241-97 X 2,148,608 2/ 39 De Stubner 241-97 2,378,432 6/45 Rethwisch et al 241-29 X 2,982,482 5/61 Curtis 241-33 3,118,622 1/64 Jones 241-97 ROBERT C. RIORDON, Primary Examiner. I. SPENCER OVERHOLSER, Examiner. 

1. A METHOD OF GRINDING SOLID PARTICLES IN A PLURALITY OF REPEATING CYCLES, COMPRISING PLACING THE MATERIAL TO BE GROUND IN SUSPENSION IN A LIQUID IN A FIRST RECEPTACLE, PASSING THE MATERIAL FROM THE FIRST RECEPTACLE INTO A GRINDER UNTIL THE FIRST RECEPTACLE IS SUBSTANTIALLY EMPTY, COLLECTING THE MATERIAL FROM THE GRINDER IN A SECOND RECEPTACLE, PASSING THE MATERIAL FROM THE SECOND RECEPTACLE BACK INTO THE GRINDER UNTIL THE SECOND RECEPTACLE IS SUBSTANTIALLY EMPTY, AND PASSING THE MATERIAL FROM THE GRINDER BACK INTO THE FIRST RECEPTACLE. 